The thunderous boom rippled across a tree-covered valley at midafternoon. China Eastern Airlines Flight MU-5735 had plunged to earth in a hilly part of rural southern China, where usually the loudest noises come from swarms of insects and villagers’ motorbikes.

At first, residents in Teng County in Guangxi region were baffled by the explosion, they told Chinese news outlets. But soon those gathering around a hillside saw the signs of what may be China’s worst air accident in decades.

Plumes of smoke floated over the clusters of bamboo and banana trees. Farmers came across shards of wreckage, apparently from the plane’s wings and fuselage, some showing the lettering of China Eastern Airlines. And villagers gathered to put out some of the fires that had broken out in the hills, one said in a telephone interview with The New York Times.

Residents told Chinese news outlets that the plane, a Boeing 737 model, plunged sharply to earth in a sparsely populated area.

According to the state-owned China News Service, a resident from the village of Molang, whom the news service cited by only his last name, Liu, said he rode his motorbike to the site with three other villagers to see if they could help with the rescue. They saw parts of the plane scattered on the site, strips of cloth hanging on trees, and a fire that stretched across more than 10 acres. But they didn’t see any remains, he told the news service.

As evening set in, the villagers waited for rescue teams to arrive in the isolated area. Nearly 1,000 firefighters, and 100 members of a local militia, have been dispatched by Chinese officials to the crash site to conduct a rescue mission.

The first rescuers to arrive began picking through debris among ferns and bamboo. As night fell, the forecast called for rain and heavy winds, weather sure to hamper the rescue effort.

At the flight’s scheduled destination, Guangzhou Baiyun International Airport, some 150 miles away, friends and relatives who had gone there to greet arriving passengers from the flight now waited for news of any survivors among the 132 onboard.